Render markdown snippets on Geo secondary sites

What does this MR do?

Fixes rendering of markdown snippets on Geo secondary sites. This fix was suggested by @fjsanpedro.

This rendering issue happens only on Geo secondary sites because snippet repos/multiple snippet files are not yet supported by Geo. This change makes a single-file snippets render as they did before new snippet code was introduced.

Closes #273510 (closed)

Screenshots

Before fix, on Geo secondary:

After fix, on Geo secondary:

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done